Polyester films have been considered to be more advantageously used in place of TAC film because they have excellent productivity, mechanical strength, and dimensional stability. Despite the above-described excellent properties, however, when polyester films are used for a roll film, they have the drawback of a poor handling property after development processing, due to a persistently remaining core set curl in the form of roll that is used for various types of photographic light-sensitive materials. Therefore, that is problem for using polyester films in the form of roll. U.S. Pat. No. 4,141,735 describes that heating of the polyester film improves the core set curl. However, it is difficult to practically use such the method, because when a bulky roll is simply subjected to heat treatment on an industrial scale, tightness of the roll, distortion, and rumples are caused, which results in a coating unevenness when photographic emulsions are subjected to a multi-layered simultaneous coating. JP-A ("JP-A" means unexamined published Japanese patent application) No. 51155/1993 describes a technique that comprises steps of winding a film into a roll so that the thickness of a gas layer lying between the film layers becomes 0.1 to 0.7 .mu.m, and then subjecting the roll of the film to heat treatment.